In recent years, there has been a considerable increase in the use of diesel engine powered automobiles because of their known advantage over gasoline powered vehicles in fuel consumption, i.e. the ability to provide more miles of vehicle travel for each gallon of fuel consumed. In view of this significant benefit and the anticipated increasing cost of engine fuels in the foreseeable future, it is expected that further significant increases in the use of diesel engines in automobiles and light commercial vehicles will be made during at least the next few years.
However, diesel engines, particularly those of the 4-stroke cycle indirect injection (prechamber) type most commonly used in automobiles and lightweight commercial vehicles, also have certain characteristics that are less favorable than those of comparable gasoline powered engines. Among these is the formation in the combustion products of carbonaceous (sooty) particulates some of which are carried with blowby gases past the pistons and piston rings into the engine crankcase and oil sump with resulting contamination of the engine lubricating oil.
Studies have indicated that diesel soot contamination has an adverse effect on certain wear-resisting additives utilized in automotive engine lubricating oils and, accordingly, the amount of soot contamination which can be accommodated in the lubricating oil charge is limited. As a result in some designs of automotive diesel engines, it has been necessary to replace the charge of lubricating oil approximately every 3,000 miles of vehicle operation as compared to a comparable oil change interval for gasoline powered vehicles of 7,500 miles. For this reason, as well as others, it is desirable to find some way of reducing the amount of particulate contamination of the lubricating oil which normally occurs during operation of automotive diesel engines.